The present invention relates to a single crystal growing apparatus and a single crystal growing method for manufacturing dislocation-free single crystal of silicon by the pulling CZ (Czochralski) method.
In general, in a single crystal growing apparatus or a single crystal pulling apparatus based on the pulling CZ method, the pressure in a space within a highly pressure-proof airtight chamber is reduced to about 10 Torr and fresh argon (Ar) gas is introduced into it At the same time, polycrystal in a quart crucible disposed in the lower portion of the chamber is heated and melted, and a seed crystal is immersed into the surface of this melt. While the seed crystal and the quartz crucible are rotated and moved up and down, the seed crystal is pulled up. Then, a single crystal rod (the socalled ingot) is grown, which comprises an upper cone portion in conical shape with its upper end protruding under the seed crystal, a body portion in cylindrical shape, and a lower cone portion in conical shape with its lower end protruding.
As a method for growing a single crystal as described above, Dash method is known in the art According to this method, with the purpose of eliminating dislocation (to turn to dislocation-free) which occurs to the seed crystal due to thermal shock when the seed crystal is immersed into the surface of the melt, pulling rate is relatively increased after the seed crystal has been immersed into the surface of the melt. As a result, a neck portion with diameter smaller than the diameter of the seed crystal, e.g. diameter of 3 to 4 mm, is formed, and the pulling of the upper cone portion as described above is started.
To solve the problem that it is not possible to pull up the single crystal of large diameter and heavy weight (150 to 200 kg or more), a method is proposed, for example, in Japanese Patent Publication 5-65477. According to this method, a neck portion with smaller diameter is formed by Dash method. Then, pulling rate is relatively decreased to form a portion with larger diameter. Next, pulling rate is relatively increased to form a portion with smaller diameter. As a result, xe2x80x9ca spherical portion with larger diameterxe2x80x9d is formed. By gripping the portion with larger diameter using grippers, the single crystal of large diameter and heavy weight is pulled up. Conventional type apparatuses for gripping the portion with larger diameter are described, for example, in Japanese Patent Publications 7-103000 and 7-515.
There are other conventional examples such as a method to grip the body portion without forming the xe2x80x9cportion with larger diameterxe2x80x9d is disclosed, for example, in Japanese Patent Publications Laid-Open 5-270974 or 7-172981. Also, there is a method for forming xe2x80x9can annular portion with larger diameterxe2x80x9d having a diameter larger than the diameter of the body portion between the upper cone portion and the body portion and for gripping this xe2x80x9cannular portion with larger diameterxe2x80x9d instead of forming the xe2x80x9cspherical portion with larger diameterxe2x80x9d as described above, and this is proposed in Japanese Patent Publications Laid-Open 63-252991 or 5-270975. In these conventional methods, gripping members with tops, which can be opened or closed, are used to grip the lower end of the portion with larger diameter of the single crystal. Such gripping members must have a certain strength under high temperature condition, and metallic member made of molybdenum is used, for example.
Japanese Patent Publication Laid-Open 10-95697 discloses a method for engaging and holding the portion with larger diameter formed for holding single crystal rod under 550xc2x0 C. or lower in the single crystal growing apparatus. This method is based on the experimental data that silicon neck may be ruptured from the seed reducing portion and slip dislocation may occur in the single crystal under the temperature higher the above temperature.
In case silicon single crystal of heavy weight is grown, the temperature of 550xc2x0 C. is too low to engage and hold the silicon single crystal. However, the single crystal can be engaged and held only at the temperature of 550xc2x0 C. or lower. If the growing crystal is gripped and stress is applied under the temperature higher than the above value, plastic deformation may take place on the crystal, and dislocation may occur in the growing crystal. Further, when such dislocation occurs, strength of the single crystal is decreased, and there may arise possibility of rupture in the subsequent process of single crystal growth.
On the other hand, with rapid development and progress to produce and use devices of highly integrated design, there are strong demands to increase the diameter of single crystal to be grown in the single crystal growing apparatus. In case single crystal with larger diameter is grown, the crystal may have heavy weight even when the single crystal is pulled up slightly. In this respect, it is desirable to engage and hold the single crystal in a stage as early as possible, i.e. when the portion with larger diameter is at high temperature.
To solve the problems of dealing with a single crystal of heavy weight and of achieving engagement and holding of the portion with larger diameter at high temperature, it is an object of the present invention to provide a method and an apparatus, by which it is possible to grow a single crystal rod of heavy weight and large diameter in dislocation-free and stable condition and to pull up the single crystal without damaging the crystal habit line of the single crystal and without causing deformation and interlaminar peeling due to the applied load. It is accomplished by finding the relation between the temperature of the portion with larger diameter and weight of the single crystal rod as required for engagement and holding of the single crystal and by finding that engagement and holding of the portion with larger diameter can be achieved at high temperature.
To attain the above object, the present invention provides a single crystal growing apparatus for pulling up single crystal, by which single crystal can be engaged and held by controlling temperature T (xc2x0 C.) in such manner as to satisfy the relabon:
Wxe2x89xa6xe2x88x92(4/3)T+1270
where T is temperature of the gripping portion to grip the portion with larger diameter, and W (kg) is weight of single crystal engaged with and held by the single crystal gripping members, under the condition that a contact member made of a material having Shore hardness of not less than 70, Vickers hardness of not more than 100, and tensile strength of not less than 400 MPa is used on a portion of the single crystal gripping members, which is brought into contact with the lower part of the portion with larger diameter, and minimum diameter of a constricted portion under the portion with larger diameter is set to 12 mm or more.
Specifically, the present invention provides a single crystal growing apparatus, which comprises a chamber with a quartz crucible disposed therein, a quartz crucible for melting a melt to be used as raw material for a single crystal, a seed crystal lift mechanism for moving a seed crystal up and down above the quartz crucible, and single crystal gripping members arranged movably in upward and downward directions in the chamber, whereby the seed crystal lift mechanism is used to immerse the seed crystal into a melt in the quartz crucible and to pull up the seed crystal, and to form a single crystal neck portion, a portion with larger diameter of single crystal, and a constricted portion under the portion with larger diameter, and a single crystal rod, and the single crystal gripping members are used to pull up the single crystal by gripping the portion with larger diameter from below and to pull up the single crystal after the portion with larger diameter of the single crystal has been formed; and
there is provided means for controlling temperature T (xc2x0 C.) to satisfy the relation:
Wxe2x89xa6xe2x88x92(4/3)T+1270
where T is temperature of the gripping portion to grip the portion with larger diameter, W (kg) is weight of single crystal engaged with and held by the single crystal gripping members, and T is between 500xc2x0 C. and 800xc2x0 C. under the condition that:
a contact member made of a material having Shore hardness of not less than 70, Vickers hardness of not more than 100, and tensile strength of not less than 400 MPa is used on a portion of the single crystal gripping members, which is brought into contact with the lower part of the portion with larger diameter, and minimum diameter of a constricted portion under the portion with larger diameter is set to 12 mm or more.